Current polling suggests there'd be a somewhat decent chance of us remaining.
Certain factors would work for each side in any hypothetical referendum. Leave would benefit from the argument that they won before, and that we supposedly just need to get on with it...in that sense Remain would have to fight hard to ensure they're not being perceived as anti-democratic or patronising to those who have different opinions from them.
At the same time though I do think there's a greater liking of the EU among those who want to Remain though because they've actually had to consider what the alternative is, and in that sense there'd perhaps be a more positive campaign as opposed to the defensive one Cameron and co mounted. I reckon the current uncertainty across the water would probably make the Northern Irish warier of leaving, and pure demographic shifts would benefit Remain too...old people skew more anti-EU than the young and even two or three years will have seen a lot of people who voted Leave pass away.
Again, all hypothetical's though.